Synthesis and characterization of UV-curable branched polyurethane acrylates via thiol-ene click reactions

In this study, UV-curable silane-based branched polyurethane acrylates (PUAS) were synthesized via thiol-ene photo-click reaction, their films and coatings were prepared and their properties were investigated. PUAS synthesis was carried out in three steps. In the first step, polyurethane prepolymers with active isocyanate ends were obtained by reacting polyol with an aliphatic diisocyanate, and in the second step, polyurethane acrylate (PUA) resins were obtained by capping the active isocyanate ends with a hydroxy functional acrylic monomer. In the third step, PUAS films and coatings were obtained by photo-click reaction of the alkene units in these resins with a silane-based thiol under UV irradiation. In PUAS structures; Hexamethylene diisocyanate (HDI), as diisocyanate; Propylene glycol (PG), Trimethylolpropane (TMP), Pentaerythritol (PENTA), as polyol; 2-hydroxyethyl methacrylate (HEMA), 2-hydroxyethyl acrylate (HEA), 3-Hydroxypropyl methacrylate (HPMA) as hydroxy functional acrylic monomers and (3-Mercaptopropyl)trimethoxysilane (MPTMS) as thiol were used. In addition, S-PUAS films were prepared as a result of sol-gel reaction of PUAS films and R-PUAS films were prepared with the addition of reactive diluent. FT-IR, TGA, DSC and SEM techniques were used in the characterization of the prepared films and coatings. Properties of the obtained films and coatings such as chemical structure, microphase behavior, micro structure, thermal stability, glass transition temperature, water repellency (contact angle), gloss, pencil hardness, chemical resistance in different solutions and solvents and gel content were investigated. The changes in the general properties of UV-curable PUA coatings caused by changes in the polyol and hydroxy functional acrylic monomer structure and a silane-based monomer, the use of reactive diluents and the sol-gel process have been extensively investigated and it is thought that the obtained results will make significant contributions to the relevant literature and the polymer and coating industry sectors.